The Ebola virus (EBOV) is a Category A bioterrorism threat for which no vaccines or small- molecule therapeutics are known. EBOV is very virulent and can cause up to 90% mortality in infected individuals. Few small molecules have been studied for their activity against EBOV, because of the stringent BSL4 conditions needed for containment of this pathogen. Of the compounds that have been investigated, a series of carbocyclic nucleosides (in which the natural C-O-C bonds are replaced by C-C-C bonds) has proven to be the most promising starting point. The carbocyclic nucleosides neplanocin A (NPC) and 3-deazaneplanocin (3- deazaNPC), in particular, demonstrated excellent activity against EBOV in in vitro and in vivo assays. The hypothesis of this proposal is that modifications to the structure of 3-deazaNPC, particularly changes in the heterocyclic base, will provide compounds with increased antiviral activity and/or reduced cytotoxicity with respect to 3-deazaNPC. The overall goal of this proposal is to develop novel carbocyclic nucleosides as therapeutics for the bioterrorist threat EBOV. The specific objective of this proposal is to optimize the structure of 3-deazaNPC to increase the antiviral activity against EBOV and reduce the cytotoxicity to produce an advanced lead compound, which can be further developed into an effective treatment for EBOV infections. No specific therapies are currently available for the treatment of EBOV. The major milestone of this proposal will be the identification of a carbocyclic nucleoside with potent (IC50 = 5 ?M) anti- EBOV activity in an infectious virus (BSL4) assay, and low (CC50 = 100 ?M) cytotoxicity, which will be further developed in a Phase II SBIR grant. Subsequent development will ideally lead to the identification of a clinical development candidate. This proposal has the following specific aims and milestones: PUBLIC HEALTH RELEVANCE: The objective of this proposal is to chemically modify the known Ebola virus (EBOV) inhibitor 3- deazaneplanocin to produce compounds with greater antiviral activity and/or lower cytotoxicity. Traditional medicinal chemistry and structure-based drug design will be used, where warranted, to make the desired improvements. The overall goal of this proposal is to develop novel carbocyclic nucleosides as therapeutics for the Category A bioterrorist threat EBOV.